Trip device for circuit breaker



April 25, 1957 T. w. BUTLER, JR 3,316,373

TRIP DEVICE FOR CIRCUIT BREAKER Filed Dec. 8, 1965 I 2 Sheets-Sheet lINVENTOR.

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Apnl 25, 1967 T. w BUTLER, JR 3,316,373

TRIP DEVICE FOR CIRCUIT BREAKER Filed Dec. 8, 1965 2 Sheets-Sheet I; /J5g #4 1 p INVEN OR. $077741; ME? 671, 9.

liability is United States Patent 3,316,373 TRIP DEVICE FOR CIRCUITBREAKER Thomas W. Butler, Jr., Ann Arbor, Mich., assignor to MechanicalProducts, Inc., Jackson, MiclL, a corporation of Delaware Filed Dec. 8,1965, Ser. No. 512,440 3 Claims. (Cl. 200-116) This invention relatesgenerally to electric circuit breakers, and more particularly to animproved trip device for an electric circuit breaker. Automatic electriccircuit breakers generally comprise a pair of separable contacts, areleasable operating mechanism that effects separation of the contacts,and a trip device responsive to predetermined electrical conditions inanelectrical circuit to effect release of the operating mechanism.

Generally, the trip device comprises a latch mechanism and a currentresponsive element that ettects movement of the latch mechanism to arelease condition. Both of these components must satisfy certain basicrequirements in order that the circuit breaker be positive in operation,durable, and consistent in performance.

The latch mechanism should have a relatively large latch overlap topreclude spurious unlatching due to, for example, vibration, yet mustunlatch the operating mechanism upon relatively slight movements of thecurrent responsive member. The current responsive member must besensitive to relatively slight current variations above a specificpredetermined level and have a usable mechanical responsecharacteristic.

It has long been a problem to produce a relatively inexpensive andcompact trip device for a circuit breaker of relatively low currentrating having a significant mechanical response characteristic ordisplacement yet be responsive to relatively small overloads.

An improved trip device for a circuit breaker, in accordance with theinstant invention, exhibits a relatively large mechanical displacementdue to relatively minute elongation of an electrically conductive wirehaving a positive temperature coefficient of expansion. The wire ismechanically connected to a rotatable beam in such a manner that anincremential elongation of the wire permits a substantial movement of alatching face on the beam in a direction substantially normal to thelongi- 'tudinal axis of the wire. The geometry of the trip device issuch that friction is minimized between the relatively moving parts,calibration is easily achieved, and remaximized.

Accordingly, one object of the instant invention is an improved tripdevice for a circuit breaker.

Another object is a trip device having a large mechanical response dueto relatively small overload currents.

' Other objects and advantages of the present invention will becomeapparent from the following description taken in conjunction with theaccompanying drawings, wherein:

FIGURE 1 is a sideelevational view of a single pole circuit breaker withone side of the housing therefor removed;

FIG. 2 is a view of the trip device removed from the circuit breaker;

FIG. '3 is a view taken in the direction of the arrow of FIG. 2; and

FIG. 4 is a view taken in the direction of the arrow 4 of FIG. 2.

As best seen in FIGURE 1 of the drawings, an electric circuit breakercomprises an insulating housing 12 molded from, for example, Bakelite. Apair of terminals 14 and 16 extend from the housing 12 for connection toopposite sides of an external electric circuit.

The terminal 16 extends inwardly of the housing 12 for the support of afixed contact 20. A movable contact 22 is aligned and engageable withthe fixed contact 20 to complete an electrical circuit through thecircuit breaker 10 comprising the terminal 16, the fixed and movablecontacts 20 and 22, a pigtail 24, a current responsive trip devicegenerally designated by the numeral 26, pigtail 28 and the oppositeterminal 14.

The operating mechanism for the circuit breaker 10 is conventional inconstruction and, in brief, comprises a manual operator or plunger 29that extends externally of and is slidably supported by the housing 12for in and out movement. The manual operator 29 comprises an innerplunger portion 30 having a lower end 31 that extends into a guideway 32formed in a lower wall 34 of the housing 12. A transversely extendingpin 36 is fixedly supported by the housing 12 and extends through a slot33 in v the plunger portion 31 so as to guide the manual operator 29 forreciprocation.

A pin 40 is supported on an upper end portion 42 of the inner plunger 30and extends through a slot 44 in an outer plunger portion 46 of themanual operator 29. The pin 40 and slot 44 function as a lost motionconnection between the inner and outer plunger portions 30 and 46 of themanual operator 29.

The inner plunger 30 has a molded central hub portion 48 that is rigidlyaffixed thereto for the support of a rotatable latch lever 70, as willbe described.

The outer plunger portion 46 of the manual operator 29 extends through aferrule '49 in a front wall 50 of the housing 12 and has a knob 52secured thereto. The knob 52 is preferably formed from an insulatingmaterial, for example, Bakelite, and is shaped to facilitate manualoperation of the circuit breaker 10.

The inner plunger portion 30 of the manual operator 29 is normallyresilient urged upwardly, as seen in FIG. 1, by a tensioned coil spring62 having one end portion 64 connected to the latch lever 70 and anopposite end portion 72 connected to 'a link member 74 that is pivotallyconnected to a bell crank 76. The bell crank 76 is pivoted on a pin 78journaled in bearing plate 80.

The bell crank 76 carries a roller 88 that is normally biased by thespring 62 clockwise into complementary notches 90 and 92 in the innerand outer plunger portions 30 and 46 of the manual operator 29,respectively. The spring 62 is sufficiently strong so that when it istensioned to the position illustrated in FIGURE 1, it holds the roller88 in the notches 90 and 92 and thereby restrains the outer plungerportion 46 of the manual operator 29 from movement outwardly of thehousing 12 and the inner plunger portion 30 from movement upwardly, asseen in FIG. 1, under the bias of the spring 62.

However, when tension of the spring 62 is relieved upon automaticopening of the circuit breaker 10, as will be described, the innerplunger shaft 30 is released for upward movement under the reduced biasof the spring 62. Movement of the roller 88 outwardly of the notches 90and 92 is also effected upon upward movement of the outer plungerportion 46 due to manual operation of the circuit breaker 10.

The latch lever 70 is pivotally supported by a pin that extends throughthe hub 48 on the inner portion 30 of the manual operator 29. The latchlever '70 has a latching surface 102 thereon that overlies acomplementary latching surface 104 on the trip device 26, to bedescribed.

Upon disengagement of the latching surfaces 102 and 134 on the latchlever 70 and trip device 2 6, respectively, the latch lever '70 rotatescounterclockwise to carry the movable contact 22 out of engagement withthe fixed contact 2% thereby to break an electrical circuit through thecircuit breaker 10. It is to be noted that the movable contact 22 ismounted on a contact carrier 105, a spring J 106 effecting a downwardbias thereon relative to the' latch lever 7 t) to provide contactpressure.

In accordance with the instant invention the trip device 26 comprises agenerally U -shaped frame 110 defined by a bight portion 112 and spacedleg portions 114 and 116. The leg portions 114 and 116 have circularstuds 118 and 120 thereon, respectively, for acceptance in complementarycircular sockets (not shown) in the housing 12 of the circuit breaker.The rotative position of the frame 110 relative to the housing 112 iscontrolled by a calibration screw 122 (FIG. 1) that is engageable withan upstanding flange 124 on the frame 110.

A generally U-shaped beam 130 defined by a bight portion 132 and spacedleg portions 134 and 136 is pivotally secured to the leg portions 114and 116 of the frame 118 by a pin 138. The pin 138 extends through theleg portions 114 and 116 of the frame 110 at points intermediate thestuds 118 and 120 and the bight portion 112 thereon.

A trip device spring 14% is secured to the beam 130 as by a pair ofrivets 142 and 144, an end portion 146 of the spring 140 having aportion 147 that extends through a complementary aperture 148 in thebight portion 112 of the frame 116) to exert a clockwise bias on thebeam 130 relative to the frame 110 as seen in FIG. 2 of the drawings.

Rotation of the beam 130 relative to the frame 110 is controlled by acurrent responsive extensible wire 150, an upper end portion 152 ofwhich is secured to the bight portion 112 of the frame 110 and a lowerend portion 153 of which is secured to an insulating grommet 154 whichin turn is secured to the bight portion 132 of the beam 130. A flexibleelectrical connector 160 is electrically connected to the end portion153 of the wire 150 and a flexible electrical connector 152 is connectedto the frame 110 to complete an electrical circuit through the tripdevice 126. A suitable heater 162 is preferably wound about the wire 150to speed up the response thereof.

A latch bar 170 is secured to a latch bar spring 172 as by a pair ofrivets 174. The latch bar 170 contains the latching surface 104,discussed hereinbefore, that supports an end portion 102 of the latch 70. Rotation of the frame 11%) under the bias of the spring 140 uponelongation of the Wire effects movement of the latch bar 170 to the leftas seen in FIGS. 1 and 2 of the drawing to effect release of the latchlever 70. It is to be noted that the latch bar 170 can be biased to theleft as seen in FIG. 1 of the drawing, by the end portion 102 of thelatch 70 to effect relatching due to the inherent resilience of thespring 172.

Manual operation of the circuit breaker 10 is effected by pullingupwardly on the knob 52 on the outer plunger portion 46 of the manualoperator 29. Upward movement of the outer plunger portion 46 effectscamming of the roller 88 to the right, as seen in FIG. 1 of thedrawings, permitting the inner plunger portion 30 of the manual operator29 to move upwardly and carry the latch 70 and movable contact 22upwardly.

The contacts and 22 of the circuit breaker 10 are closed by pushingdownwardly on the knob 52 of the outer plunger portion 46.

Automatic opening of the circuit breaker 10 due to an overload or shortcircuit condition is achieved by elongation of the current responsivewire 159 which permits the beam portion 136 of the trip device 26 torotate clockwise under the bias of the trip device spring Clockwiserotation of the beam 130 carries the latch surface 104 on the latch barto the left, as seen in FIG. 2 of the drawings thereby freeing the latch70 for counterclockwise rotation under the bias of the spring 62 toseparate the movable contact 22 from the fixed contact 20.Counterclockwise rotation of the latch 170 reduces the bias of thespring 62 on the bell crank 76 and roller 88 freeing the manual operator29 for movement upwardly to the contacts open condition.

It is to be understood that the specific construction of the improvedtrip device for a circuit breaker herein disclosed and described ispresented for the purpose of explanation and illustration and is notintended to indicate limits of the invention the scope of which isdefined by the following claims.

What is claimed is:

1. An electric circuit breaker comprising, a housing, a pair ofseparable contacts in said housing, a releasable operating mechanismmounted on said housing and operable to effect separation of saidcontacts,

a trip device frame, means adjustably supporting said frame on saidhousing,

a beam pivotally secured to said frame,

a latch on said beam engageable with said operating mechanism,

resilient means mounted on said beam for normally biasing said beam forrotation relative to said frame, and,

- a current responsive wire having a positive temperature coefficient ofexpansion connected to and extending between said frame and beam,elongation of said wire allowing said beam to rotate relative to saidframe under the bias of said resilient means to retract the latchingsurface on said beam from engagement with the operating mechanism of thecircuit breaker.

2. A trip device for an electric circuit breaker in accordance withclaim 1 wherein;

said frame is of generally U-shaped configuration defined by spaced legportions having a bight portion therebetween,

said beam is of generally U-shaped configuration defined by a bightportion and spaced leg portions, the leg portions of said beam beingpivotally secured to the leg portions of said frame, respectively, and

said current responsive wire is connected to and extends between thebight portions of said frame and beam, respectively.

3. A trip device for an electric circuit breaker in accordance withclaim 1 wherein;

said resilient means comprises a leaf spring carried by said beam, and

said latch is mounted on said spring so as to facilitate engagement ofsaid operating mechanism therewith.

No references cited.

BERNARD A. GILHEANY, Primary Examiner.

H. B. GILSON, Assistant Examiner.

1. AN ELECTRIC CIRCUIT BREAKER COMPRISING, A HOUSING, A PAIR OFSEPARABLE CONTACTS IN SAID HOUSING, A RELEASABLE OPERATING MECHANISMMOUNTED ON SAID HOUSING AND OPERABLE TO EFFECT SEPARATION OF SAIDCONTACTS, A TRIP DEVICE FRAME, MEANS ADJUSTABLY SUPPORTING SAID FRAME ONSAID HOUSING, A BEAM PIVOTALLY SECURED TO SAID FRAME, A LATCH ON SAIDBEAM ENGAGEABLE WITH SAID OPERATING MECHANISM, RESILIENT MEANS MOUNTEDON SAID BEAM FOR NORMALLY BIASING SAID BEAM FOR ROTATION RELATIVE TOSAID FRAME, AND,